This invention relates to methods of attaching ferrules to the outer circumferential surface of optical fibers to act as terminations and/or connectors for said fibers and more particularly to a method of ferrule attachment involving welding by laser irradiation.
For industrial application purposes, optical fibers are commonly terminated with plastic ferrules. This is done, for example, so that small diameter optical fibers can be positioned with respect to optical couplers and the like.
It is known to bond optical fibers to plastic ferrules through the use of adhesives, such as with epoxies, by mechanical crimping and by welding using an irradiation source such as a laser. Epoxy bonding is an exacting process which requires high precision in formulating, applying and curing the epoxy. Crimping is also a mechanically exacting process which, if incorrectly done, can adversely impact the optical and/or structural characteristics of the fiber. Welding is typically carried out using a plastic ferrule which is transparent to the laser radiation and a jacket on the optical fiber which fits snugly within the ferrule and which is much more absorbent to the laser radiation. This approach, however, results in highly asymmetric heating and a weld pool which is composed substantially entirely of material from the fiber jacket. Such an asymmetric weld is often mechanically weak and will not stand up to either application temperature extremes or mechanical stress created by rough handling or environmental conditions.
The present invention, in one aspect, is an improved method of welding plastic ferrules to plastic jacketed optical fibers. According to this aspect of the invention, a plastic jacketed optical fiber is provided in combination with the plastic ferrule so that the outer circumferential surface of the plastic jacket is in juxtaposed relationship to an inner circumferential surface of the ferrule. A layer of material is placed between and in contact with the two juxtaposed surfaces, which material is substantially more absorptive to radiation at a predetermined wavelength than the materials of both of the jacket and ferrule. In the preferred embodiment, the plastic material of the ferrule is substantially transparent to the predetermined wavelength radiation, whereas the material of the intermediate layer is highly absorptive as a result of its optical content. Thereafter, the combination is irradiated substantially at said wavelength to create a weld pool which, according to the preferred aspects of the invention, is highly symmetrical and extends in substantially equal amounts to equal depths into the materials of both the jacket and the ferrule. The radiation is typically from a laser.
In accordance with the second aspect of the invention, a ready-to-weld plastic jacketed optical fiber is provided. In accordance with the invention, an exposed outer surface of a plastic jacket surrounding the optical fiber is coated either circumferentially continuously or discontinuously with a second transitory material whose absorptivity to radiation at a predetermined wavelength is much higher than that of the plastic material on which it is placed. This combination is ready to place within the confines of a plastic ferrule which itself is also transparent to the predetermined wavelength radiation and which is sized to fit over and in contact with the intermediate transitory material. That combination may then be irradiated and welded as described above.
The terms xe2x80x9cplasticxe2x80x9d and xe2x80x9cpolymerxe2x80x9d are used interchangeably in this document.
Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawing.